G.Ting-Kuo Fey

Synthesis of non-stoichiometric lithium nickel cobalt oxides and their structural and electrochemical characterization

Non-stoichiometric phases of lithium nickel cobalt oxides were synthesized by a sol–gel method using oxalic acid as a chelating agent. The structural properties have been examined using X-ray diffraction techniques. Electrochemical coin cell studies showed materials with excess lithium stoichiometry had interesting properties of improved capacity and cyclability. Of all the compositions with excess lithium stoichiometry, Li1.1Ni0.8Co0.2O2, showed better electrochemical characteristics with a first cycle discharge capacity of 182 mAh/g and a 10th cycle of 172 mAh/g than the ideal stoichiometry LiNi0.8Co0.2O2. The structural and electrochemical properties of LixNi0.8Co0.2O2 with x=1.00, 1.05, 1.10 and 1.15 are discussed in detail.

Electrochemical performance of Sr2+-doped LiNi0.8Co0.2O2 as a cathode material for lithium batteries synthesized via a wet chemistry route using oxalic acid

Oxalic acid assisted sol–gel synthesis of Sr2+-doped LiNi0.8Co0.2O2 has been reported for the first time. Structural characterization was carried out using X-ray diffraction studies. Electrochemical studies were performed by assembling 2032 coin cells with lithium metal as an anode. The charge–discharge studies were performed galvonostatically at a 0.1 C rate from 3.0–4.2 V. Of all the doped compositions with dopant mole ratios ranging from 10−8 to 10−4, the compound with a dopant mole ratio of 10−6 showed improved capacity and cyclabilty with a first cycle discharge capacity of 173 mAh/g and 10th cycle of 167 mAh/g. The improvement in capacity has been discussed using a defect model.

Malonic acid-assisted synthesis of LiNi0.8Co0.2O2 cathode active material for lithium-ion batteries

Polycrystalline LiNi0.8Co0.2O2 was synthesized by a solution route with malonic acid as the complexing agent. The effects of temperature, duration of heat treatment, pH of the precursor solution, and the nature of the solvent employed on the performance characteristics of the product were studied. It was observed that a 12-hour 800 °C heat treatment protocol was necessary to obtain products with optimal electrochemical characteristics. Furthermore, an excess lithium stoichiometry of 1.05 was found to be detrimental to the performance of the cathode material. The beneficial effect of ethanol as a solvent over water on the product characteristics is explained by the presence of solvent molecules in the coordination sphere of the cations. A pH of 7, at which malonic acid is complexed completely with the cations without interference from other nucleophiles, was found to be ideal for the synthesis of the cathode active material from aqueous solutions. With ethanol as the medium, the product formed by a 12-h calcination at 800 °C yielded a first-cycle capacity of 173 mAh/g and a tenth-cycle capacity of 169 mAh/g.

The effect of varying the acid to metal ion ratio R on the structural, thermal, and electrochemical properties of sol–gel derived lithium nickel cobalt oxides

Abstract The lithiated nickel cobalt oxide LiNi 0.8 Co 0.2 O 2 was synthesized using citric acid as a chelating agent by a sol–gel method. The effect of varying the acid to metal ion ratio R on the structural, thermal, and electrochemical properties of the synthesized compound were studied. The discharge capacity of LiNi 0.8 Co 0.2 O 2 synthesized with an acid to metal ion ratio R =1 was 187 and 176 mAh/g for the 1st and 10th cycles, respectively. Increasing the R value to 2 resulted in a decrease in capacity to 170 mAh/g for the 1st cycle and 161 mAh/g after 10 cycles. A further increase in R value to 3 did not cause any appreciable improvement in the electrochemical performance of the cell. However, there was no decrease in capacity or cyclability compared to the compound synthesized at R =1. The structural, thermal, and electrochemical performance of the materials synthesized at different R values are compared and discussed.